Coaxial cable termination



Sept. 29, 1959 J. w. DRENNING COAXIAL. CABLE TERMINATION Filed Dec. 4,1956 W l l l 1 l I l M l ll i l h o IIHHHUIIIIIIIIIIII'I 1L4 0 r kw M Ewm 2 V2 0 m0 r w B M W h J Y United States Patent COAXIAL CABLETERMINATION John W. Drenning, Baltimore, Md., assignor to KoppersCompany, Inc., a corporation of Delaware Application December 4, 1956,Serial No. 626,123 6 Claims. (Cl. 174-73) This invention relates toapparatus for terminating coaxial cable transmission lines, and moreparticularly to apparatus for terminating solid dielectric coaxial cabletransmission lines which are used to transmit high voltages to equipmentsuch as electrostatic precipitators.

Various types of cable terminal arrangements have been used in the pastin connection with transmission lines for high frequency signals.Although these arrangements have proven satisfactory in accommodatingthe low voltages used for high frequency signals, they have not provenentirely satisfactory in the transmission of high voltages which tend tocause large stresses in the terminals. Furthermore, past arrangementsfor terminating solid dielectric coaxial lines have employed some formof dielectric material in their assembly, which material has had to beheated, poured around the cable, and allowed to solidify. This procedurehas required great care in its execution in order to prevent thepossible occurrence of air voids which cause voltage breakdowns. As aresult, the procedure has been costly in both time and labor.

The present invention provides an apparatus for terminating coaxialcable which avoids the above-mentioned disadvantages, which iseconomical and straightforward in its construction and maintenance, andwhich eliminates past difficulties in coaxial cable splicing andterminating.

More specifically, the present invention provides coaxial cableterminating apparatus which utilizes a compartment filled with aninsulating fluid medium to eliminate air voids in the compartment and toprevent destructive corona discharge and spark-over between the internalhigh voltage parts disposed in such compartment and the grounded metalcontainer which forms the compartment. The present invention furtherprovides a standard porcelain through-bushing, a portion of whichprojects into the compartment and through which high voltage may besafely conducted to equipment destined to be energized; a mechanicalfitting which serves to grasp the outer conductor of a coaxialdielectric cable to hold the cable in position and which at the sametime electrically connects the outer conductor to ground; a soft metalsealing medium for the fluid insulating compartment which also serves tosecure the terminal portion of the cable to the insulating compartment;and, a terminal which is apart from the insulating through-bushing andnot disposed therewithin so as to necessarily require completereplacement upon the failure of such throughbushing. Further, thepresent invention provides a cornplete terminal assembly which is soarranged that in case of a failure of any one of the components, suchdefective component can be swiftly replaced by even a person withoutparticular skill in terminal assemblies.

Various other features of the present invention will become obvious toone skilled in the art upon the reading of the disclosure set forthhereinafter.

More particularly, the present invention provides a pothead forterminating a solid dielectric coaxial cable having an inner and outerconductor comprising: an insulat- 2,906,809 Patented Sept, 29, 1959 ingcompartment; a terminal arrangement in the wall of the compartment toterminate the outer conductor and to permit the inner conductor of thecable to pass therethrough into the compartment, the terminalarrangement including an outer sleeve member, first and second innersleeve members through which the inner conductor of the cable passesinto the compartment, the inner sleeve members being spaced inend-to-end relationship and movable relative each other, with the firstinner sleeve member having a portion in spaced concentric relation withthe outer sleeve member and having the outer wall of such portion soshaped with respect to a portion of the inner wall of the outer sleevemember to form a gripping wedge for the outer conductor of the coaxialcable, and with the second inner sleeve member having a portion of itsouter wall in movable contact with a portion of the inner wall of theouter sleeve member to urge the first inner sleeve member into grippingrelation with the outer conductor of the cable; and a sealing ringdisposed between the first and second inner sleeve members andsurrounding the inner conductor to firmly grip the inner conductor whenthe ring is pressure displaced between the inner sleeve members.

It is to be understood that various changes can be made, by one skilledin the art, in the arrangement, form, and construction of the apparatusdisclosed herein without departing from the scope or spirit of thisinvention.

Referring to the drawings:

Figure l is a schematic elevational view of a portion of anelectrostatic precipitator, including the coaxial cable potheadarrangement of the present invention;

Figure 2 is an enlarged detailed cross-sectional view of the coaxialcable pothead arrangement broadly disclosed in Figure 1;

Figure 3 is an enlarged detailed view of the outer conductor terminalportion of the arrangement disclosed in Figure 2;

Figure 4 is an enlarged view of a coaxial cable which has been preparedfor connection to the pothead arrangement.

Referring to Figure l of the drawings, an electrical precipitatorhousing 2 is disclosed. Housing 2 has disposed therein a plurality ofdischarge electrodes 3 which cooperate with collecting electrodes (notshown) spaced therefrom in a manner well-known in the art. As is alsowell-known in the art, discharge electrodes 3 are supported by a framearrangement which includes horizontal conducting bars 4 from which thedischarge electrodes are suspended. Horizontal conducting bars 4 are, inturn, suspended by means of vertical conducting bars 6 and each verticalconducting bar 6 is supported from the top of the housing by having itsupper threaded extremity pass through an aperture in conducting bar 7,the bar 6 being held in place on bar 7 by nut 8 fastened to the threadedextremity of bar 6. Bar 7, in turn, is supported by porcelain insulator9 fixed to the roof of housing 2. A hood 11 serves to protect thesuspension framework.

Passing through a passage in the side wall of hood 11 is a portion of aporcelain through-bushing 12, the through-bushing 12 being connected tobar 7 by means of jumper 13. The remaining portion of the porcelainthrough-bushing projects into coaxial cable pothead arrangement broadlydesignated by the reference numeral 14, the pothead arrangement beingattached to the hood 11 in a manner described hereinafter. It is to beunderstood that the apparatus so far described is substantiallyconventional in the art and therefore specific details have not been setforth.

Referring to Figures 2 and 3 of the drawings, the inventive coaxialcable pothead arrangement is disclosed.

It is to be understood that the disclosed arrangement, inaddition tobeing useful with electrostatic precipitators,

can be used in conjunction with other electrical equipment which alsomight require high voltages.

The pothead includes cylindrical housing 16, welded at 17 to plate 18.Plate 18 is bolted by means of bolts 19 to plate 21, agasket 22 beingprovided between plate 18 and plate 21. Plate 21 is connected by nut andbolt assemblies 23 to the above described hood 11 of the precipitatorhousing, the plate serving to cover passage 24 in the hood. A passage 26is provided in plate 21. This passage communicates with passage 24 andpermits a portion of the porcelain through-bushing 12 to project intothe insulating compartment 27, which is formed by:

the cylindrical housing 16 of the pothead. I A collar 28 surrounds thethrough-bushing 12 and is cemented thereto, an additional cement-liketype of material being provided as at 31 to retain the through-bushingto the flange of the collar. This collar is attached to plate 21 bymeans of bolts 29. Bolts 29 pass through the aforementioned gasket 22, aportion of which is also positioned between the collar shoulder andplate 21.

On the top portion of cylindrical housing 16, a fluid port 32 isprovided, the fluid port being surrounded by ring 33 welded to the outerWall of the housing. Attached to the ring by means of tap bolts 34 iscover plate 36. When the cover plate is removed, an insulating fluidmedium can be introduced into the insulating compartment 27. The fluidmedium can be any type of electrical insulating oil I which has a highdielectric strength and which advantageously is adequate to withstandhigh temperatures. For example, transformer mineral oil has been foundto be satisfactory. The insulating oil serves to avoid spaces of airwhich would otherwise exist and performs the insulating function aroundthe inner conductor of a coaxial cable which passes into compartment 27,as will be described hereinafter. Thus, destructive corona discharge andsparkover between the inner conductor which carries high voltage andcylindrical housing 16 which is grounded (as is also describedhereinafter) is prevented. To provide for possible expansion of the oilsin the compartment due to temperature changes and to prevent outsidedirt from entering into the compartment, a oneway ball valve 37 islocated in cover plate 36 at the top of cylindrical housing 16.

Positioned at the bottom of housing 16 is a drain valve assembly 38.This drain valve serves to drain the insulating oil from compartment 27when repairs are required or when a sampling of insulating oil isdesired.

Passing through the through-bushing 12 is an electrical conductor rod39, one end of which projects slightly beyond the bushing and intocompartment 27. Washer 41 is welded at 42 to this end of the rod and agasket 43 is provided between this washer and the corresponding end ofbushing 12. The other end of conductor rod 39, which lies on the outsideof compartment 27, is threaded to receive nut and washer assembly 44 towhich the aforedescribed jumper 13 is attached. Assembly 44 also servesto hold rod 39 firmly in place in bushing 12. As can be seen in Figure 2of the drawing, the inner conductor of a polyethylene insulated coaxialcable (to be described in detail hereinafter) is connected to the end ofthe conductor rod 39 which projects into the insulating compartment 27.This is accomplished by providing a socket 46 at this end of the rod,the inner conductor being held in place in the socket by set screw 45passing through the side of the conductor rod and contacting the innerconductor to complete full contact between it and the rod. It is to benoted that with the rod and through-bushing arrangement disclosed,failure of the porcelain-bushing does not necessarily result in cablefailure since the cable is apart from the porcelain and not containedWithin it, as has been the case with graded cable potheads of the past.

In order that the inner conductor of a coaxial cable may pass intoinsulating compartment 27, a terminal arrangement is provided at theside wall of the cylindrical housing 16 for terminating the outerconductor and to permit the inner conductor to pass therethrough intothe compartment. This terminal arrangement includes an outer sleevemember 51, one end of which is internally threaded to engage theexternal threads of an inner sleeve member 52. Sleeve member 52 extendsthrough the side wall of cylinder 16 and has a portion thereofprojecting into the insulating compartment with the remaining portionfalling outside the compartment. The sleeve 52 is provided with an outershoulder 53 which abuts the outer wall of the cylinder 16 and which iswelded thereto at 54. It is to be noted that the passage in the. portionof the sleeve member 52 which projects into compartment 27 is flaredoutwardly toward the end as at 56. This serves to relieve any extremevoltage stresses on the oil in the compartment and on the polyethyleneinsulation of the inner conductor (to be described hereinafter).

The other end of sleeve member 52 is recessed to receive a soft leadseal ring 57.

Upon tightening of the terminal arrangement, ring 57 will be displacedby'pressure so as to grip the inner insulating polyethylene which itsurrounds to form an oiltight junction between the cable and the housingand to provide additional securement of the cable to the housing. Tocompress and displace the seal ring 57an inner sleeve member 58 isprovided on the side of ring 57 opposite the side which abuts the recessof inner sleeve member 52. Inner sleeve member 58 is in endto-endrelation and movable relative sleeve member 52, sleeve member 58 beingdisposed within and in spaced concentric relation with outer sleevemember 51. At that end of sleeve member 58 which abuts the lead sealring 57, there is provided a raised wedge portion 59 adapted to bite into the soft lead seal ring and insure the displacement thereof. .In thisconnection, it is to be noted that the body of member 53 adjacent member52 is of slightly larger diameter than the diameter of the recess forring 57 in member 52. This is desirable in order to prevent too muchdisplacement of the ring 57 when sleeve member 51 is tightened, theparts being so arranged that the ring 57 seals the unit upondisplacement but does not distort the polyethylene insulation of thecable described hereinafter. The opposite end of inner sleeve member 58is provided with a tapered outer wall portion 61, the tapered wall beingadapted to cooperate with a swept back portion 62 on the inner side ofthe collared end 63 of outer sleeve member 51. An outer shoulder 64 isprovided on inner sleeve member 58, this outer shoulder having a greaterdiameter than the maximum diameter of the swept back portion 62 of thecollared end 63 to thus abut against the collared end when the terminalarrangement is tightened. When such terminal arrangement is tightened,the outer conductor of a coaxial cable and the outer insulation of theconductor is gripped between the swept back portion 62 of the outersleeve member 51 and the tapered portion 61 of the inner sleeve member(as will be described in detail hereinafter). To eflect such tighteningin a swift and efiicient manner, the outer sleeve member 51 is providedwith apertures 66 around the outer wall to receive the tines of aspanner-type tightening wrench.

One end of a ground wire 67 is attached to the end wall of housing 16,this ground wire having its other end attached to the metallic shield ofa coaxial dielectric cable as described hereinafter.

Referring to Figure 4 of the drawing, a polyethylene insulated coaxialcable broadly designated by reference numeral 71 is disclosed. Thiscable includes an inner copper conductor 72 surrounded by an innerpolyethylene insulation 73. Surrounding the inner polyethyleneinsulation 73 is an outer conductor 74 in the form of copper braid, andsurrounding the outer conductor is an outer polyethylene insulation76. Ametallic armor shield 77 surrounds the outer insulator 76.

In a typical example wherein a coaxial cable such as disclosed in Figure4 is prepared for installation in the pothead disclosed in Figures 1-3,the armor shield 77 is stripped back and cut off about from the end. Theouter polyethylene insulation 76 and copper braid 74 are stripped backand cut oil about 8%" from the end. The inner polyethylene insulation 73is cut olf about from the end. When this has been accomplished, thecable is ready to be connected to the pothead terminal arrangement.

The outer sleeve member 51 is slipped over the prepared end of thecable. The inner sleeve member 58 is passed over the inner polyethyleneinsulation 73, the tapered portion 61 of the inner sleeve member beingforced under the copper braid 74. The lead seal ring 57 is slipped overthe inner polyethylene insulation 73 and is pushed back until it touchesthe wedge 59 of the inner sleeve 58. The prepared end 73 of the coaxialcable is then passed through the inner sleeve member 52 and the innercopper conductor 72 is connected to the steel rod 39 by inserting itinto socket 46 and tightening the set screw42. When this has beenaccomplished, the outer sleeve member 51 is then rotated so that thelead seal 57 is displaced between the two inner sleeve members 52 and 58to form an oil-tight junction between the inner polyethylene insulation73 and to provide additional securement of the cable to the housing. Atthe same time, the tightening of the terminal arrangement serves to gripthe outer conductor 74 and outer insulation 76 between the taperedportion 61 of the inner sleeve member 58 and the swept back portion 62of the collared end 63 of outer sleeve 51.

Thus, the coaxial cable is connected to the pothead in a swift andeflieient manner with a minimum of operation and a minimum of hazard.When the connection has been completed, the insulating compartment 27 isfilled with an insulating oil to eliminate any air voids and to preventspark-over between the conductor which carries high voltage and thehousing 16 which is grounded.

With the above described arrangement a complete pothead assembly isobtained having components which can be replaced in case of failure in aminimum of time, and with a minimum of effort and skill by virtue of thestraightforwardness of the several parts of the assembly.

The invention claimed is:

l. A pothead for terminating a solid dielectric coaxial cable having aninner conductor and insulation surrounding the same and outer conductorand sheath comprising:

an insulating compartment; a terminal arrangement in the wall of saidcompartment for terminating said outer conductor and to permit saidinner conductor of said cable to pass therethrough into saidcompartment, said terminal arrangement including an outer sleeve member,first and second inner sleeve members through which said inner conductorpasses into said compartment, said inner sleeve members being inend-to-end relationship and axially movable relative to each other, saidfirst inner sleeve member having a portion in spaced concentric relationwith said outer sleeve member and the outer wall of such portion shapedwith respect to a portion of the inner wall of said outer sleeve memberto form a gripping wedge for said outer conductor of said cable, saidsecond inner sleeve member having a portion of its outer wall in movablecontact with a portion of the inner wall of said outer sleeve member tourge said first inner sleeve member into gripping relation with saidouter conductor and sheath of said cable, and a sealing ring disposedbetween said first and second inner sleeve members and surround ing saidinner conductor and insulation to firmly grip said inner conductorinsulation when pressure displaced between said inner sleeve members.

2. A pothead for terminating a solid dielectric coaxial cable having aninner conductor and insulation surrounding the same and outer conductorand sheath comprising: an insulating compartment for said innerconductor, said compartment having an insulating fluid medium disposedtherein; an insulated through-bushing, at least a portion of which isdisposed within said fluid medium of said compartment; a terminalarrangement in the wall of said compartment for terminating said outerconductor and to permit said inner conductor of said cable to passtherethrough into said compartment through said fluid medium and intocontact with said insulated bushing, said terminal arrangement includingan outer sleeve member, first and second inner sleeve members throughwhich said inner conductor passes into said compartment, said innersleeve members being spaced in end-to-end relationship and axiallymovable relative each other, said first inner sleeve member having aportion in spaced concentric relation with said outer sleeve member andthe outer wall of such portion shaped with respect to a portion of theinner wall of said outer sleeve member to form a gripping wedge for saidouter conductor of said cable, said second inner sleeve member having aportion of its outer wall in movable contact with a portion of the innerwall of said outer sleeve member to urge said first inner sleeve intogripping relation with said outer conductor and sheath of said cable,and a sealing ring disposed between said first and second inner sleevemembers and surrounding said inner conductor and insulation to form aseal therearound when pressure displaced between said inner sleevemembers.

3. A pothead for terminating a solid dielectric coaxial cable having aninner conductor and insulation surrounding the same and outer conductorand sheath comprising: an insulating compartment for said innerconductor, said compartment having an insulating fluid medium disposedtherein; an insulated through-bushing, at least a portion of which isdisposed within said fluid medium; a conductor rod passing through saidthrough-bushing, a terminal arrangement in the wall of said compartmentfor terminating said outer conductor of said cable to pass therethroughinto said compartment, through said fluid medium and into contact withsaid conductor rod, said terminal arrangement including an outer sleevemember, first and second inner sleeve members through which said innerconductor passes into said compartment, said inner sleeve members beingspaced in end-to-end relationship and axially movable relative eachother, said first inner sleeve member having a portion in spacedconcentric relation with said outer sleeve member and the outer wall ofsuch portion shaped with respect to a portion of the inner wall of saidouter sleeve member to form a gripping wedge for said outer conductor ofsaid cable, said second inner sleeve member having a portion of itsouter wall in movable contact with a portion of the inner wall of saidouter sleeve member to urge said first inner sleeve into grippingrelation with said outer conductor and sheath of said cable, and asealing ring disposed between said first and second inner sleeve membersand surrounding said inner conductor and insulation to form a sealtherearound when pressure displaced between said inner sleeve members.

4. A terminal arrangement for terminating the outer conductor of a soliddielectric coaxial cable having an inner conductor and insulationsurrounding the same and outer conductor and sheath comprising: an outersleeve member, first and second inner sleeve members through which saidinner conductor passes, said inner sleeve members being positioned inend-to-end relationship and axially movable relative each other, saidfirst inner sleeve member having a portion in spaced concentric relationwith said outer sleeve member and the outer wall of such portion spacedwith respect to a portion of the inner wall of said outer sleeve memberto form a gripping wedge for said outer conductor of said cable, saidsecond inner sleeve member having a portion of its outer wall in movablecontact with a portion of the inner wall of said outer sleeve member tourge said first inner sleeve into gripping relation with said outerconductor and sheath of said cable, and a sealing ring disposed betweensaid first and second inner sleeve members and surrounding said innerconductor and insulation to firmly grip said inner conductor whenpressure displaced between said inner sleeve members.

5. A terminal arrangement for terminating the outer conductor of a soliddielectric coaxial cable having an inner conductor and insulationsurrounding the same and outer conductor and sheath comprising: an outersleeve member, first and second inner sleeve members through which saidinner conductor passes, said inner sleeve members being spaced inend-to-end relationship and axially movable relative each other, saidfirst inner sleeve member having a portion in spaced concentric relationwith said outer sleeve member and the outer Wall of such portion shapedwith respect to a portion of the inner wall of said outer sleeve memberto form a gripping wedge for said outer conductor of said cable, saidsecond inner sleeve member having a flared inner wall portion at thepoint where said inner conductor leaves said second sleeve, said secondinner sleeve also having a portion of its outer wall in movable contactWith a portion of the inner wall of said outer sleeve member to urgesaid first inner sleeve into gripping relation with said outer conductorand sheath of said cable and a compressible sealing ring disposedbetween said first and second inner sleeve members and surrounding saidinner conductor and insulation to firmly grip said inner conductorinsulation when pressure displaced between said inner sleeve members.

6. A pothead for terminating a solid dielectric coaxial cable having aninner conductor and insulation surrounding the same and outer conductorand sheath comprising: an insulating compartment for said innerconductor, said compartment having a fluid medium disposed therein; aninsulated through-bushing, at least a portion of which is disposedwithin said fluid medium; a conductor rod passing through saidthrough-bushing; a terminal arrangement in the wall of said compartmentfor terminating said outer conductor and to, permit said inner conductorof said cable to pass therethrough into said compartment, through saidfluid medium and into contact with said conducting rod, said terminalarrangement including an outer sleeve member, first and second innersleeve members through which said inner conductor passes into saidcompartment, said inner sleeve members being spaced in end-to-endrelationship and movable relative each other, said first inner sleevemember having a portion in spaced concentric relation with said outersleeve member and having the outer wall of such portion shaped withrespect to a portion of the inner sleeve wall of said outer sleevemember to form a gripping wedge for said outer conductor of saiddielectric cable, said second inner sleeve member having a flared innerwall at that point in which said inner conductor leaves said innersleeve member, said second inner sleeve member also having a portion ofits outer wall in threaded engagement with a portion of the inner wallof said outer sleeve member so as to be able to urge said first innersleeve member into gripping relation with said outer conductor andsheath of said cable, and a compressible sealing ring disposed betweensaid first and second inner sleeve members and surrounding said innerconductor and insulation to firmly grip said inner conductor insulationand form a seal therearound when pressure displaced between said innersleeve members.

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